This invention relates generally to the construction of valves used for controlling the flow of various fluids, including liquids and gas.
It is common practice in the construction of valves (gate or ball) to employ seat rings that are accommodated in recesses provided in the valve body and which are spring-urged toward the movable valve member. One difficulty that has been experienced with such valves, particularly when used in systems handling petroleum liquids, is that sediment tends to accumulate behind the seat rings, thereby limiting their range of movement. This may make opening and closing movements of the valve member difficult, particularly when the valve is of the short gate type. As shown in U.S. Pat. No. 3,807,688, granted Apr. 20, 1974, spreader means can be provided to maintain a minimum spacing between the seat rings when a short gate is moved to open position. This is of benefit in preventing accumulation of sediment to the extent of interfering with closing of the gate, but it does not prevent such accumulation of sediment as may materially restrict movements of the seat ring relative to the body. Also, while the spreader means shown in the above-mentioned patent is effective, it is somewhat difficult to install with proper alignment during assembly of the valve. Also under certain conditions it may permit some cocking of the seat rings when the gate is in open position.